Phenothiazine in prill form and method for making the same

ABSTRACT

Phenothiazine and its derivatives products are provided with a minimal level of fines or dust as a result of forming such products in prill form. The prills are generally spherical. Also provided is a method for reducing the level of powder in phenothiazine product which includes forming the phenothiazine product in prill form such that the prills have a generally spherical shape. The prill product achieves improved handling, flowability and dissolution times, while minimizing the generation of phenothiazine fines and dust, and the problems associated with worker exposure, irritation and sensitization to such fines and dust.

This application is a continuation of U.S. patent application USSN09/453,685, filed Dec. 3, 1999, the priority to which is claimed, nowU.S. Pat. No. 6,284,279.

BACKGROUND OF THE INVENTION

Phenothiazine is typically manufactured in flake form. Such flakes areformed by coating molten phenothiazine onto a drum flaker, where theproduct is cooled, and crystallizing the product to a solid which isflaked. The product is then conveyed to a physical separation process inwhich the product fines (powder) are separated from the flakes typicallyby the use of sizing screens. The product is then packaged and shippedto customers who convey or transfer the flakes through their ownprocessing equipment. Despite product classification, the flakes tend tocontain up to about 6% of product fines after manufacture. Further, theflakes are prone to further breakdown into fines during subsequentshipping and handling.

The generation of product fines or powder in the flake phenothiazineproduct presents problems. Flake products containing such fines sufferfrom the deficiencies of non-uniform particle size, caking, dustinessand clumping. Phenothiazine is a respiratory, skin, eye andgastrointestinal irritant and skin sensitizer, and is more likely tocause such problems when in the form of fines. Product fines in theflake product also increase the likelihood of product explosiveness.Flake product containing high levels of powder (i.e., greater than about6% particles having a particle size of less than about 500 microns) isalso prone to caking or clumping.

Non-uniform particle size in flaked product increases the tendency ofthe product to cake and/or clump and to resist ready flow transfer bothinternally and at customer facilities. The caking and/or clumping of theproduct makes it difficult to discharge from containers such as bins,bags, trucks, storage silos and the like and difficult to transfer. Itmay also have a tendency to bridge or block in containers. Product finesalso present safety, health and environmental issues. From a safetystandpoint, product fines are of particular concern due to the increasedrisk of explosion, as well as increased risk to employee health withrespect to increased risk of skin irritation and skin sensitization andthe like as noted above.

In accordance with the foregoing, there is a need in the art for amethod to produce phenothiazine which reduces the problems associatedwith powder and fines in the finished product, but which still produceshigh quality phenothiazine. There is also a need in the art to reducethe problems associated with caking and/or clumping of phenothiazineproduct during shipment, transfer and storage.

BRIEF SUMMARY OF THE INVENTION

The invention includes a solid phenothiazine product, comprising aplurality of phenothiazine prills, wherein said prills are generallyspherical.

The invention further includes a method of reducing the level of powderin phenothiazine product, comprising forming the phenothiazine productin prill form such that the prills have a generally spherical shape.

The invention also includes a solid phenothiazine product comprising aplurality of phenothiazine prills, wherein the prills are generallyspherical and the product has no greater than about 6% by weight powder.

The invention includes a method for making phenothiazine in prill form,comprising introducing molten phenothiazine into at least one nozzlehaving a plurality of holes to form molten phenothiazine droplets; andcooling the droplets to form solid prills. The invention also includes asolid phenothiazine product formed by that method.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe preferred embodiments of the invention, will be better understoodwhen read in conjunction with the appended drawings. For the purpose ofillustrating the invention, there are shown in the drawings embodimentswhich are presently preferred. It should be understood, however, thatthe invention is not limited to the precise arrangements andinstrumentalities shown. In the drawings, like numerals are used toindicate like elements throughout. In the drawings:

FIG. 1 is a schematic representation of a method for makingphenothiazine prills in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention is directed to phenothiazine product having improvedproperties and reduced levels of fines, or powder, which is in prillform as well as to a method for making the phenothiazine product. Theinvention is further directed to a method for reducing the level ofpowder in phenothiazine product.

In accordance with the invention, a phenothiazine product is provided inprill form, wherein the prill form is generally spherical. The prillsare formed by providing a molten phenothiazine feed into at least onenozzle having a plurality of holes to form molten phenothiazine dropletswhich are cooled to form prills. The feed material for forming themolten phenothiazine may be any available form of phenothiazine.Phenothiazine is a solid material which is currently commerciallyavailable in both flake and powder forms, however, other forms to bedeveloped which could be formed into molten phenothiazine feed may alsobe used. As used herein, phenothiazine feed material may be anyphenothiazine material, provided it is in solid form and can be made tobe in a molten form, for example through application of heat.Phenothiazine for use as feed typically has a molecular weight of 199.26and a chemical formula of C₁₂H₉NS. The commercially availablephenothiazine typically has a melting point of 184° C. and a boilingpoint of 371° C. The bulk density is about 0.85 for flake product andabout 0.75 for powder. The chemical formula is as follows:

As used in this application, “phenothiazine” includes phenothiazine andits analogs and derivatives, including without limitation, compoundshaving formula (II) as shown below.

wherein R¹, R², and R³ may be the same or different and may be hydrogen;halogens, such as chlorine and fluorine and the like; branched orstraight chain, and substituted or unsubstituted hydrocarbon groups suchas alkyl, alkenyl, or alkynyl groups of from 1 to 26 carbon atoms;substituted and unsubstituted aryl groups and aralkyl groups; orfunctional groups, including, but not limited to sulfonyl, carboxy,amine, alkylamine, hydroxy, carboxy, silyl, siloxy; and other similarderivatives and their salts. Substituted groups for hydrocarbon, aryland aralkyl groups may include any of the above functional groups aswell as elements such as oxygen, sulfur, silicon, nitrogen, and thelike. Most preferably R¹, R² and R³ in formula (II) are hydrogen. Informula (II), m and n are preferably independently from about 1 to about4.

To form the prills, the phenothiazine feed in molten form, which may bephenothiazine in accordance with formulas (I) and/or (II) as well asphenothiazine derivatives, preferably those in accordance with formula(II), is fed into a jet priller capable of receiving a moltenphenothiazine feed and passing the feed through nozzles having aplurality of holes. The basic method for forming the products of theinvention is described with reference to FIG. 1.

The molten phenothiazine is preferably first melted at a temperature ofpreferably from about 205° C. to about 215° C. and under nitrogenpressure, then conditioned at a preferred temperature of about 200° C.at pressures of from about 1.5 to 3 bar when fed into the jet prilleralso under a nitrogen atmosphere. While these conditions are preferredfor forming phenothiazine in accordance with formula (I), the conditionsmay be varied in accordance with the ordinary skill in the art to adjustfor different, optimal melt temperatures for different grades ofphenothiazine and for phenothiazine derivatives.

As the phenothiazine is fed to the priller head, it is preferably alsofirst filtered to remove foreign material. As the feed passes throughthe holes, it is cooled to a solid, generally spherical, prill shape,preferably by very rapid chilling using liquid nitrogen and/or nitrogengas. The use of nitrogen is important in order to maintain productquality and to achieve a yellow colored product. However, it should beunderstood, based on this disclosure, that other cooling gases,preferably other inert cooling gases, may be used to form phenothiazineprills according to the invention, however, a nitrogen gas is necessaryfor maintaining the preferred yellow color. Flow through the holes iscontrolled by pressure in the prill generator which is heldsubstantially constant at between 0 and 1 bar. The feed is broken intodroplets of from about 1 mm to about 2 mm by use of a resonance nozzlewhich is vibrated using a stroboscope at a frequency of from about 100to about 1500 Hz, and preferably from about 400 to about 1100 Hz. Thedroplets then fall through a cryogenic freezing column where they arecooled immediately by liquid nitrogen into partially crystalline prillsas they fall through the column. The column is also maintained under acooled nitrogen atmosphere. The prills leaving the column are atapproximately from about 120° C. to about 170° C., more preferably about140° C., and pass into a spiral cooler which further cools and completescrystallization of the prills. In addition, the prills are separatedfrom fines or dust along with nitrogen gas.

The separated nitrogen gas is chilled and is recycled to the coolingportion of the jet priller. The prill form product is removed from thejet priller and is useful for many applications, particularly those inwhich phenothiazine powder is problematic. FIG. 1 includes a flowdiagram representation of the basic process for forming thephenothiazine prills using a jet priller as described above. A preferredjet priller is commercially available and/or prills can be manufacturedusing a jet priller from GMF Gouda, Goudsche Machinefabriek, B. V. inWaddinzveen, Holland, sold as Model JP15.

The phenothiazine prill product of the invention may be used in a widevariety of applications, including as a stabilizer for a variety ofchemical applications. The product may also be used for an inhibitor,antioxidant and shortstopping agent in a variety of diverse applicationssuch as the stabilization of acrylic acids, esters and monomers or as astabilizer for chloroprene monomer/neoprene polymer, styrene monomer andother vinylic monomers. The prill product is also useful as anantioxidant in synthetic lubricants and oils, polyols for polyurethanesand polyester and vinyl ester resins. In addition, phenothiazine is auseful pharmaceutical intermediate. Due to its high level of activity,it functions at very low concentrations and enhances the functioning ofother stabilizers. It will also function well in strongly acidicenvironments as well as in both air or nitrogen environments.

The prill products of the invention preferably have less than about 6%and more preferably less than about 1% by weight powder, wherein“powder” is a reference to product fines and/or powder particulateshaving particle sizes of less than about 500 microns. Further, theprills preferably have an average diameter as measured in the longestdimension of the prills of from about 0.5 mm to about 2.3 mm and morepreferably from about 1 mm to about 2 mm. The generally sphericalphenothiazine prills in accordance with the product formed in accordancewith this invention have significantly improved flow characteristics dueto the size uniformity and are safer to use than standard phenothiazineproducts in flake or powder form.

The invention will now be described in further detail with respect tothe following non-limiting examples.

EXAMPLE 1

Experimental, small-scale simulation of phenothiazine prills wasundertaken on a laboratory scale apparatus. A one liter, 3-neck reactorflask was used to simulate a flaker feed tank. It was equipped withnitrogen feed, a stirrer for agitation, a temperature probe and a bottomoutlet. The apparatus was vacuum evacuated and nitrogen purged threetimes prior to product loading under nitrogen. The reactor was thencharged, and the phenothiazine flake heated under nitrogen to a moltenstate at about 200° C. The molten phenothiazine was then slowly drippedthrough the bottom outlet valve (a simulated nozzle) into approximatelyone liter of liquid nitrogen (at about −192° C.) in a vacuum jacketedDewar flask. Bright yellow prills were formed and subjected to selectiveanalyses. The bright yellow prills met all product specifications,evidenced no precipitate, and handled in a manner and with an efficiencysimilar to standard phenothiazine flake product.

EXAMPLE 2

A larger scale trial was then undertaken. Phenothiazine product wascharged to a holding vessel. The product was then melted at temperaturesnoted below, and conveyed under 3.1 bars pressure to a receiver vessel.The product was then fed into the prilling head of a Model JP15/1Closed-Loop jet priller from GMF Gouda having 100 nozzles with a nozzlediameter of about 0.5 mm. The product flow was controlled by keeping thepressure in the jet priller head constant. In the prilling head, theproduct was broken into 1-2 mm droplets as passed through the nozzle.The nozzles contained between about 100 to 250 holes and flow throughthe nozzle was controlled by setting a vibrating membrane with the aidof a stroboscope at a frequency of 1005-1007 Hz. The product was forcedthrough the holes and prills were formed. Prills were formed byimmediate liquid nitrogen cooling of the molten droplet into a solidprill form. The molten feed was at approximately 200° C. (ranginggenerally from about 194.7 to 195.5° C.) and the liquid nitrogentemperature was about −192° C. The product solidified into a prill as itfell through the liquid/nitrogen gas environment in the cryogenicfreezing column. Further cooling occurred on the spiral fluid bed, afterwhich the product was discharged from the unit. Any generated productfines were removed by use of a cyclone. Nitrogen was recirculated backinto the main unit after passing through a gas cooler. The trialresulted in the product of bright yellow prills which met all standardproduct specifications, evidenced no precipitate, and generated efficacysimilar to standard phenothiazine flake product. The prills alsoofferred improved handling and flowability.

The prills as formed were generally spherical in shape and had anaverage diameter of about 1 mm. The prills also had a low angle ofrepose and exhibited a very narrow particle size distribution. Lowpowder levels of less than 1% were achieved, and the product was notprone to caking. The product also evidenced flow, transfer and handlingcharacteristics equivalent to or superior to the existing flake product.Additionally, due to the more uniform shape and smaller average particlesize, the prills demonstrated an enhanced dissolution time in comparisonto flake product. A comparison of the properties of standard flake andthe prills formed in this Example are shown below in Table 1.

TABLE 1 Flake Prill Properties Appearance Yellow Flakes Yellow PrillsMelting Point ° C. 184 min. 184.9 min. Purity (%) 99.6 99.9 Angle ofRepose 36 25 Bulk Density 0.8 0.77 Jar Shake Test for Powder Slight toHeavy Nil to Very Slight Thickness (mm) 1.40 1.65 Average Diameter (mm)N/A 1 Particle Size Distribution ≧2360 microns 75 0 <2360 to 500 microns19 99 <500 microns 6 1 Dissolution Time Acetone (min.) 5 3 MethylMethacrylate (min.) 12.5 11 Butyl Acrylate (min.) 8 5.5 Product Efficacy(hours to polymerize 13 14 methyl methacrylate)

Based on the foregoing, prills of phenothiazine were formed whichattained properties which were at least comparable to those of standardphenothiazine products, and in most cases improved in comparison withstandard phenothiazine products, and advantageously provided asubstantially uniform average diameter and narrow particle sizedistribution as well as a very low level of fines. Such characteristicsprovided reduced incidences of caking and/or clumping and demonstratedimproved flow properties in transport and in use. Other significantadvantages obtained by using the prills include improvements toenvironmental and workplace safety as well as a reduction in the cost ofmanufacturing resulting from the low level of fines.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

I claim:
 1. A phenothiazine product, comprising a plurality ofphenothiazine prills, wherein the prills are generally spherical andyellow.
 2. The phenothiazine product of claim 1 wherein the prills havea melting point of 184.9° C. minimum.
 3. The phenothiazine product ofclaim 2 wherein the prills have a purity of 99.9%.
 4. The phenothiazineproduct of claim 3 wherein 99% by weight of the prills have a sizebetween 500 microns to 2360 microns.
 5. The phenothiazine product ofclaim 4 wherein less than 1% by weight of the prills have a particlesize less than 500 microns.
 6. A phenothiazine product, comprising aplurality of phenothiazine prills, wherein the prills are generallyspherical, are yellow, have a melting point of 184.9° C. minimum, andthe prills have a particle size distribution such that 99% of the prillshave a size of from 500 microns to 2360 microns.
 7. The phenothiazineproduct of claim 5 wherein the prills have a purity of 99.9%.
 8. Aphenothiazine product comprising a plurality of phenothiazine prills,wherein the prills are generally spherical, yellow, have a melting pointof 184.9° C. minimum and a purity of 99.9% and a particle sizedistribution such that about 99% of the prills have a size of from 500microns to about 2360 microns.
 9. The phenothiazine product of claim 8wherein less than 1% by weight of the prills have a particle size lessthan 500 microns.
 10. A phenothiazine product comprising a plurality ofphenothiazine prills, wherein the prills are generally spherical, areyellow, have a melting point of 184.9° C. minimum, less than 1% byweight of the prills have a particle size less than 500 microns, and theproduct has a angle of repose of
 25. 11. A method for makingphenothiazine in generally spherical prill form comprising: (a)introducing molten phenothiazine feed into a jet priller capable ofreceiving a molten phenothiazine feed and passing the feed through atleast one nozzle which has a plurality of holes to form moltenphenothiazine droplets; and (b) cooling the droplets to form solidphenothiazine prills.
 12. The method of claim 11, wherein said moltenphenothiazine is produced by melting phenothiazine at from about 205° C.to about 215° C. under nitrogen atmosphere.
 13. The method of claim 12wherein said molten phenothiazine is conditioned at about 200° C. at apressure of from 1.5 to 3 bar; and introduced into said jet priller alsounder nitrogen atmosphere.
 14. The method of claim 13, wherein saidmolten phenothiazine is filtered to remove foreign material.
 15. Themethod of claim 11 wherein said droplets are cooled to a solid generallyspherical, prill shape by an inert cooling gas.
 16. The method of claim15 wherein said droplets are cooled to a solid generally spherical,prill shape by liquid nitrogen and/or nitrogen gas.
 17. A method formaking a phenothiazine product in generally spherical prill formcomprising: (a) charging phenothiazine product to a holding vessel; (b)melting said product; (c) conveying the molten product to a receivervessel; (d) feeding said molten product into the prilling head of a jetpriller and forcing the molten product through said holes; (e)controlling the flow through the nozzles by means of a vibratingmembrane so as to form 1-2 mm droplets of molten product; (f) permittingsaid droplets to immediately fall through a cryogenic freezing column soas to form solid prills; (g) further cooling said prills; and (h)removing any generated fines.
 18. The method of claim 17 where in step(c) the molten product is conveyed at about 200° C. and at a pressure of3.1 bars.
 19. The method of claim 18 where in step (d) said prillinghead has 100 nozzles with a nozzle diameter of 0.5 mm, each nozzlehaving 100 to 250 holes.
 20. The method of claim 19 where in step (e)said membrane is vibrating at a frequency of 1005-1007 Hz.
 21. Themethod of claim 20 where in step (f) said cryogenic freezing columncontains a coolant mixture comprising liquid nitrogen/nitrogen gas. 22.The method of claim 21 where in step (g) said further cooling is in aspiral fluid bed.
 23. A method for making a phenothiazine product ingenerally spherical prill form comprising: (a) charging phenothiazineproduct to a holding vessel; (b) melting said product; (c) conveying themolten product at about 200° C. and a pressure of about 3.1 bars to areceiver vessel; (d) feeding said molten product into the prilling headof a jet priller having 100 nozzles with a nozzle diameter of 0.5 mm,each nozzle having 100 to 250 holes and forcing the molten productthrough said holes; (e) controlling the flow through the nozzles bymeans of a membrane vibrating at a frequency of 1005-1007 Hz so as toform 1-2 mm droplets of molten product; (f) permitting said droplets toimmediately fall through a liquid nitrogen/nitrogen gas cryogenicfreezing column so as to form solid prills; (g) cooling said prillsfurther in a spiral fluid bed; and (h) removing any generated fines bymeans of a cyclone.
 24. A method of making phenothiazine in prill formcomprising: feeding molten phenothiazine into a nozzle which has aplurality of holes to form molten phenothiazine droplets, cooling thedroplets with an inert gas or liquid to form solid yellow phenothiazineprills, and maintaining said prills in an inert nitrogen atmosphere. 25.The method of claim 24 wherein the inert gas or liquid is nitrogen. 26.The method of claim 24 which further comprises separating said prillsfrom fines and dust.